First improvements of handles for screwdrivers made of a hard plastic material have been suggested in U.S. Pat. No. 2,871,899 directed to improvements of the haptics of the handle. Here, a separate cover layer for the handle made of a soft plastic material is slid on a core of the handle. For a transfer of torsional moment in circumferential direction both the core of the handle and the cover layer of the handle comprise correlating profiles for a positive engagement. The use of the soft plastic material for the cover layer of the handle improves the grip of the handle. However, tests in the practical field have shown that the soft cover layer separates from the hard core under heavy loads and builds folds. The aforementioned separation of the cover layer from the core of the handle is also called “tumbling”. In particular intense use of such handle leads to the painful development of blisters at the palm of the hand of the user and to increased stresses of the bones of the hand that might lead to inflammations.
In order to avoid the aforementioned drawbacks, in the following it has been suggested to adhere the core of a handle with the cover of the handle wherein the soft plastic only builds segments of the outer surface of the handle or completely covers the handle in circumferential direction, cp. DE 92 02 550 U1, DE 43 04 965 A1, DE 295 15 833 U1, DE 195 39 200 A1, DE 295 17 276 U1, DE 299 00 746 U1. Today, handles of these types are manufactured by injection moulding of plastic materials. These known embodiments lead to good ergonomics and haptics of the handles for tools of increased quality. For such handles made of two components of different plastic materials a tool or functional part is anchored within a core made of a hard plastic material and the core is surrounded by injection moulding of a cover layer made of a soft plastic material, cp. European Patent No. EP 0 627 974 B1. The cover layer made of the soft plastic material comprises a certain elasticity and leads to a more pleasant grip than a handle which is formed only by a hard plastic material. Furthermore, the soft plastic material might also comprise a larger friction coefficient than a hard plastic material. As a consequence, by means of such “two-components-handle” larger torsional moments might be transferred than in case of using a handle with the same size but only made of a hard plastic material. This is in particular important for handles used for screwdrivers, screw clamps and the like.
German Patent Application No. DE 101 13 368 A1, corresponding to U.S. Pat. No. 6,220,128 B1, is directed to a handle for a hammer, wherein the handle comprises hollow chambers. Such chambers increase the elasticity of the handle. Such increased elasticity is used for improving the elastic dampening of shocks and impulses in the transfer of a force from the head of the hammer to the hand of the user. A similar embodiment is shown in German Patent No. DE 197 32 421 C2 corresponding to Canadian Patent Application No. CA 2,209,885 A1.
Similar in German Gebrauchsmuster No. DE 299 04 043 a handle is used for damping oscillations of an impact drilling machine, a grinding machine and the like.